【LeetCode】5. Longest Palindromic Substring

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example:

Input: "babad"

Output: "bab"

Note: "aba" is also a valid answer.

Example:

Input: "cbbd"

Output: "bb"

题意：求最长回文串。

思路：我是从discuss区看到的，整体思路事从用两个指针j,k从内往外遍历，当遇到不能使回文成立的条件时，更新最大值记录

class Solution(object):
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: str
        """
        if len(s)==0: return ''
        if len(s)==1: return s
        front = 0
        l = 0
        for i in range(len(s)):
            if len(s)-i<l/2: break #当后面的字符串已经不能更新最大值时
            j = k = i
            while k+1<len(s) and s[k] == s[k+1]: k += 1 #跳过一样的字符
            while j>0 and k+1<len(s) and s[j-1] == s[k+1]:  #从里往外遍历
                j -= 1
                k += 1
            if k-j+1 > l:
                front = j
                l = k-j+1
        return s[front:front+l]